Wireless communication systems have been widely deployed to provide various types of communication services such as voice or data. In general, a wireless communication system is a multiple access system that supports communication of multiple users by sharing available system resources (a bandwidth, transmission power, etc.) among them. For example, multiple access systems include a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, a Time Division Multiple Access (TDMA) system, an Orthogonal Frequency Division Multiple Access (OFDMA) system, a Single Carrier Frequency Division Multiple Access (SC-FDMA) system, and a Multi Carrier Frequency Division Multiple Access (MC-FDMA) system.
D2D communication refers to a communication scheme in which a direct link is established between User Equipments (UEs) and voice and data are transmitted between them via the direct link without intervention of an evolved Node B (eNB). D2D communication may include UE to UE communication, peer to peer communication, etc. D2D communication is applicable to Machine to Machine (M2M) communication, Machine Type Communication (MTC), etc.
D2D communication is considered as one of methods for mitigating the load of an eNB caused by rapidly increasing data traffic. For example, compared to a legacy wireless communication system, D2D communication can reduce the overload of a network because data is transmitted and received between devices without intervention of an eNB. Further, with the introduction of D2D communication, the effects of reduction of eNB processes, reduction of power consumption in D2D devices, the increase of data rate, the increase of network accommodation capability, load distribution, cell coverage extension, etc. are expected.